fix(transformer/typescript): preserve computed property key with side effects when removing class fields

babu-ch · babu-ch · commit f0affc6f4b11 · 2026-03-16T23:14:56.000+09:00
diff --git a/crates/oxc_transformer/src/typescript/class.rs b/crates/oxc_transformer/src/typescript/class.rs
@@ -209,7 +209,7 @@ impl<'a> TypeScript<'a> {
     pub(super) fn transform_class_on_exit(
         &self,
         class: &mut Class<'a>,
-        _ctx: &mut TraverseCtx<'a>,
+        ctx: &mut TraverseCtx<'a>,
     ) {
         if !self.remove_class_fields_without_initializer {
             return;
@@ -220,6 +220,13 @@ impl<'a> TypeScript<'a> {
                 && prop.value.is_none()
                 && !prop.key.is_private_identifier()
             {
+                // Keep properties whose computed keys have side effects.
+                // e.g. legacy decorator transforms `[FIELD_NAME]` to `[_a = FIELD_NAME]`,
+                // and removing the property would discard the assignment.
+                // This matches TypeScript's behavior of keeping such properties.
+                if let Some(key) = prop.key.as_expression() {
+                    return key_needs_temp_var(key, ctx);
+                }
                 return false;
             }
             true
diff --git a/tasks/transform_conformance/snapshots/oxc.snap.md b/tasks/transform_conformance/snapshots/oxc.snap.md
@@ -1,6 +1,6 @@
 commit: 87a048db
 
-Passed: 204/335
+Passed: 206/337
 
 # All Passed:
 * babel-plugin-transform-class-static-block
@@ -555,7 +555,7 @@ x Output mismatch
 x Output mismatch
 
 
-# legacy-decorators (6/86)
+# legacy-decorators (8/88)
 * oxc/class-without-name-with-decorated_class/input.ts
 Bindings mismatch:
 after transform: ScopeId(0): ["dec"]
diff --git a/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/input.ts b/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/input.ts
@@ -0,0 +1,8 @@
+const FIELD_NAME = "myField";
+
+function dec(target: any, key: string) {}
+
+class MyModel {
+	@dec
+	[FIELD_NAME]: string;
+}
diff --git a/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/options.json b/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/options.json
@@ -0,0 +1,11 @@
+{
+  "plugins": [
+    "transform-legacy-decorator",
+    [
+      "transform-typescript",
+      {
+        "removeClassFieldsWithoutInitializer": true
+      }
+    ]
+  ]
+}
diff --git a/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/output.js b/tasks/transform_conformance/tests/legacy-decorators/test/fixtures/oxc/computed-key-property-decorator/output.js
@@ -0,0 +1,7 @@
+var _FIELD_NAME;
+const FIELD_NAME = "myField";
+function dec(target, key) {}
+class MyModel {
+  [_FIELD_NAME = FIELD_NAME];
+}
+babelHelpers.decorate([dec], MyModel.prototype, _FIELD_NAME, void 0);
